My rubbish javascript code

highlightNav.js

/**
 * @todo rewrite so logic is separated out and it's testable
 * @todo Properly develop if time allows
 */
export const highlightNav = () => {
    let scrollPos = window.scrollY;
    let hashLinks = document.querySelectorAll('.js-hash-nav');

    Array.from(hashLinks).forEach((link, index) => {
        let nextElement = hashLinks[(index + 1)];
        let content = document.getElementById(link.hash.replace('#', ''));
        let nextContent = nextElement ? document.getElementById(nextElement.hash.replace('#', '')) : false;

        if (content == null) {
            return;
        }

        link.classList.remove('active');

        let offsetTop = content.offsetTop;
        let body = document.querySelector('body');
        let offsetBottom = nextContent ? nextContent.offsetTop : body.scrollHeight;

        if (index === 0 && scrollPos < offsetTop) {
            link.classList.add('active');
        } else if (scrollPos > offsetTop && scrollPos < offsetBottom) {
            link.classList.add('active');
        }
    });
};

selectNavByHash.js

/**
 * @todo Properly develop if time allows
 */
export const selectNavByHash = (window, navSelector = '.js-hash-nav', activeClass = 'active') => {
    let hash = window.location.hash;
    if (hash === '') {
        return;
    }

    let element = document.querySelector(`a[href="${hash}"]`);

    Array.from(document.querySelectorAll(navSelector)).forEach(nav => {
        nav.classList.remove(activeClass);
    });

    if (element === null) {
        return;
    }

    element.classList.add(activeClass);
};